Field of the Invention
The present invention relates to a power supply control device for inductive loads that controls the duty ratio of a power switching element connected between a DC power supply and an inductive load. In particular, the present invention relates to an improvement of a power supply control device when ground terminals of a DC power supply, an inductive load, and a power supply control device are connected to a common ground circuit through separate ground wiring lines.
Background Art
In the related art, for example, in a linear solenoid that is a part of an in-vehicle electrical load, a power switching element is interposed at the upstream position of each of a DC power supply as a vehicle battery and a linear solenoid as a plurality of inductive loads, and an excitation current for each inductive load is variably adjusted by controlling the duty ratio of the power switching element.
As a current control device for such a known electrical load, a current control device based on an external feedback control method is disclosed in which the duty ratio of a power switching element is controlled through a comparison deviation integrating circuit, which is configured by hardware, according to a conduction command signal, which corresponds to a conduction target current that is generated by a microprocessor, and a current detection signal by a current detection resistor connected in series to the linear solenoid (for example, refer to Patent Document 1).
In addition, a current control device for an electrical load based on an internal feedback control method is disclosed in which a microprocessor that sets a conduction target current controls the duty ratio of a power switching element through comparison deviation integrating means, which is configured by software, according to a current detection signal by a current detection resistor connected in series to a linear solenoid (for example, refer to Patent Document 2).
In addition, a power supply control device for an in-vehicle electrical load is disclosed in which ground terminals of an in-vehicle electrical load, which is an inductive load, and a power supply control device therefor are connected to the vehicle body and an additional connection between the ground terminals is made by the external common negative line (for example, refer to Patent Document 3).    [Patent Document 1] JP-A-2006-100509 (FIG. 1, abstract)    [Patent Document 2] JP-A-2006-238668 (FIG. 1, abstract)    [Patent Document 3] JP-A-2008-107157 (FIG. 1, abstract)
According to Patent Documents 1 and 2 described above, negative terminals of the current control device as a power supply control device, the vehicle battery as a DC power supply, and the linear solenoid as an inductive load are connected to the vehicle body, which is a common ground circuit, through separate ground wiring lines.
In addition, the current control device has an abnormality determination function. For example, when a closing command is given to the power switching element, if no voltage is applied to the inductive load, a disconnection abnormality of the switching element or the load wiring line is determined. In addition, when an opening command is given to the power switching element, if a voltage is applied to the inductive load, a short-circuit abnormality of the switching element or a short-to-power abnormality in which the positive-side load wiring line is short-circuited to the power line is determined. Thus, abnormality detection is performed for each linear solenoid.
However, there is a problem in that the current control device performs an uncertain control operation and accordingly accurate abnormality determination cannot be performed when the disconnection abnormality of the ground wiring line occurs due to poor contact of a negative terminal connector of the current control device or the loosening of a terminal of a vehicle body connecting portion of the ground wiring line, and the like.
In addition, in the case of Patent Document 3 described above, an external common negative line other than the vehicle body ground connection needs to be added between the in-vehicle electrical load as an inductive load and the power supply control device. Accordingly, there is a problem in that the wiring cost is increased.